# Finding the formula for a graph

• Apr 14th 2010, 04:59 PM
florx
Finding the formula for a graph
http://i41.tinypic.com/351gyde.jpg

I need help with finding the horizontal shift for the function P = f(t). Also how would we find the formula for this? I already know that Midline is 2100, Amplitude is 900. But I don't know how to complete this formula...
900 * sin (???) + 2100

Thanks.
• Apr 14th 2010, 05:10 PM
pickslides
The period of this function is 4

Use the fact that $\displaystyle n$ influences the period in $\displaystyle \sin(nx)$

and period is given by $\displaystyle \frac{2\pi}{n}$

so solve $\displaystyle 4=\frac{2\pi}{n}$
• Apr 14th 2010, 05:11 PM
skeeter
Quote:

Originally Posted by florx

I need help with finding the horizontal shift for the function P = f(t). Also how would we find the formula for this? I already know that Midline is 2100, Amplitude is 900. But I don't know how to complete this formula...
900 * sin (???) + 2100

Thanks.

$\displaystyle P(t) = -900\sin\left[B(t \pm C)\right] + 2100$

$\displaystyle B = \frac{2\pi}{4} = \frac{\pi}{2}$

C = phase shift ... looks close to a 0.5 shift to the left to me.
• Apr 14th 2010, 05:35 PM
florx
Hmm, I don't get how you got -900 from. The amplitude is 900. What made you put a negative in front of it? Also where did you get the 0.5 from. What formula did you use?
• Apr 14th 2010, 06:02 PM
skeeter
Quote:

Originally Posted by florx
Hmm, I don't get how you got -900 from. The amplitude is 900. What made you put a negative in front of it? Also where did you get the 0.5 from. What formula did you use?

look at the curve ... it's an inverted sine wave.

amplitude = |A|

as far as the 0.5 ... no formula, I just looked at the graph's horizontal shift.